An asset register is a list of what the business owns. It takes an afternoon to create, almost nobody has one, and it turns out to matter in four separate situations that all arrive without warning.
What goes on it
For each item of any value: what it is, make and model, serial number, where it is, who is responsible for it, when it was bought, what it cost, and — where relevant — when it was last serviced and when it is next due.
A spreadsheet is entirely adequate. Photographs of the serial plates, stored with it, cost nothing and save a great deal.
Why it matters: insurance
After a fire or a break-in, an insurer wants to know what was there and what it was worth. A register with serial numbers and purchase records makes that a submission; its absence makes it an argument you conduct from memory while trying to restart a business.
It also keeps your sums insured honest. Values drift as equipment is added, and under-insurance reduces claims proportionally.
Why it matters: tax
Wear and tear is claimed on assets over time, and your accountant needs to know what you own, when you bought it and what it cost. A register produces that in minutes rather than through a reconstruction of old bank statements.
Why it matters: theft
Recovered equipment is matched by serial number. Without one, a stolen item that turns up cannot be proved to be yours.
Internally, a register with an owner against each item makes it obvious when something has gone — which is both a deterrent and the reason things stop quietly disappearing.
Why it matters: selling or borrowing
Anybody buying the business, lending against it, or valuing it will ask what it owns. A register is the answer; a walk round the premises with a notebook is not, and it undermines confidence in everything else you present.
Keep it current with a routine
Add items when you buy them — attach it to the same moment you file the invoice. Remove them when they are sold or scrapped, and note what happened.
Then check it against reality once a year. Businesses that do this routinely find items long since broken and disposed of still listed, and occasionally items nobody can account for at all. Both are worth knowing.
Store it away from the assets
A register kept only on the computer in the building is a register that burns with it. Cloud storage, or a copy elsewhere. The whole point is that it survives the event that makes you need it.
General guidance on commercial practice, not tax or insurance advice.